1. Field of the Invention
The present invention relates generally to spark plugs, igniters, and other such ignition devices and to techniques for connecting an incoming terminal contact to the center electrode assembly of the ignition device. More particularly, the invention relates to a terminal end connection specifically designed to provide a continuous, uninterrupted electrical connection with an ignition lead or ignition coil high-voltage terminal so that the spark gap or other sensor diagnostic feature can be conducted at low voltages in the interval between sparks.
2. Related Art
Numerous types of connections have been used for electrically coupling an ignition lead to the terminal end of a spark plug. Their particular construction depends largely upon the specific application for which they are used. For instance, some spark plugs have a bulbous-shaped terminal electrode that connects with a complementary shaped protective boot located at the end of the ignition lead. Other spark plugs employ a threaded terminal electrode for attachment to an ignition lead also having a similarly threaded end. Although connections such as these have been used extensively in the industry and provide many desirable advantages, additional considerations must be taken into account when the spark plugs are used in connection with coils and high vibration applications, such as Formula 1, motorcycles, snowmobiles, etc., and further when low voltage diagnostics, such as ion sensing in the spark gap, are required to provide continuous, uninterrupted feedback to an engine computer control module. These connections must also posses the ability to quickly connect/disconnect the coil lead from the sparking device.
In coil-on-plug applications, high levels of vibration can cause the connection between the high voltage coil terminal and the spark plug terminal electrode to become non-continuous and intermittent. Though an intermittent contact does not usually prevent a higher voltage ignition pulse from transmitting through to the spark plug (as these pulses usually have a voltage ranges from 5,000 volts to 40,000 volts typically and are thus capable of bridging most small distance gaps), it can present certain problems when low voltage diagnostics are involved. Spark plugs are more frequently being used for combustion diagnostics. For example, the current in the spark gap can be monitored between firings and used as data indicative of certain aspects of the combustion process. Other examples of combustion chamber diagnostics via the spark plug might include stain gauge sensing, pressure sensing, piezo electric devices, thermocouples, etc. In such instances, it becomes more important to avoid unintended breaks in the conductive path to the spark gap, since sensing takes place at much lower voltages than is used for spark discharge. For example, ion sensing in the spark gap takes place in the range of 150–200 volts, while other diagnostic systems may require signals in the 1–50 volt ranges, and even others in the millivolt ranges.
It is an increasingly held belief that more sophisticated combustion chamber monitoring using low voltage diagnostics can, when implemented effectively, replace many of the prior art type sensing devices currently used in connection with internal combustion engines. For example, it may be possible to eliminate the crank position sensor, the oxygen sensor, or any of the other numerous sensors which typically provide feedback to a computer control module if effective and continuous condition feedback via the spark plug is provided to the computer control device. For this to be achievable, the stream of feedback information from the low voltage diagnostic equipment must be reliably continuous. Prior art connections between the coil lead wire and the spark plug center electrode include too much flexibility and inherent resiliency to achieve reliably continuous contact during high vibration situations.
An intermittent connection between the ignition coil high voltage output terminal and the spark plug terminal electrode can also accelerate wear and physical damage to the connection components. As these components intermittently contact each other, portions of the components are damaged and worn away. Additionally, the intermittent connection causes the high voltage ignition pulse traveling from the ignition lead to the spark plug to arc from one component to the other, thus causing pitting and other deterioration of the components. This is particularly true in applications employing coil-on-plug or coil-over-plug technologies, as the added mass of the coil promotes significant independent movement of the ignition lead with respect to the spark plug center electrode.
Moreover, intermittent contact between the high coil voltage terminal and the spark plug terminal can cause an increase in the emission of electromagnetic interference, or noise. Each time the connection between these to components is broken, the high voltage ignition pulse forms an arc between the two components, thereby causing a certain amount of noise to be given off. This noise may interfere with sensitive electronic circuitry located on the vehicle, and is generally undesirable.
Thus, it would be advantageous to provide a sparking device having a center wire assembly that connects to a coil terminal such that a continuous, uninterrupted, and reliable connection is established. It would also be advantageous to provide a separable coil and plug in which continuous contact is maintained between the coil high voltage and spark plug center wire assembly.